The administration of medicaments by inhalation is well-known. A wide variety of medicaments are now administered by that route, for the treatment of a range of respiratory disorders.
The most common form in which such medicaments are formulated for administration by inhalation is as a powder. In the past, many such compositions were formulated as pressurised aerosols, in which the powder medicament was suspended in a liquefied propellant. Due to the adverse environmental effects of the propellants conventionally used, however, there is now increased interest in the use of so-called dry powder inhalers (DPIs). In a DPI, a unit dose of medicament powder, either packaged as such or metered from a bulk reservoir of medicament, is presented to an airway and is then entrained in an airflow passing through the airway. The airflow is most commonly generated by the patient's act of inhalation.
DPIs, such as the CLICKHALER® inhaler produced by Innovata. Biomed in the UK and described in EP0539469B, preferably include a dose counter mechanism for providing an indication of the number of doses that have been administered to a patient and/or the number of doses that remain in the inhaler. Conventional dose counter mechanisms for use with DPIs comprise a ratchet mechanism with indicia being carried by the ratchet wheel.
WO2005/102430 discloses a dose counter mechanism for a DPI that comprises a tape carrying numbers that are visible at a tape display area. Actuation of the DPI causes the tape to index and a different number to be displayed at the tape display area, thereby giving a visual indication of the number of doses that have been dispensed.
Whilst the dose counter mechanism disclosed in WO2005/5102430 is beneficial, further improvement of it would be advantageous. In particular, it would be desirable for the dose counter mechanism to not only indicate to a user of the DPI device the number of doses that have been dispensed (or, alternatively, the number of doses that remain to be dispensed), but also to prevent continued actuation of the device after the last intended dose has been dispensed. Otherwise, a patient may continue to use the device, believing that further doses of medicament are being dispensed when in fact the device is exhausted.